(a) Technical Field
The present disclosure relates generally to vehicular control systems, and more particularly, to controlling a vehicle engine using an optimized torque map by matching the torque map to gear shifting patterns.
(b) Background Art
Generally, the term “engine map” refers to a set of one- or multi-dimensional parameter tables loaded into a vehicle control unit, e.g., electronic control unit (ECU), to control various engine parameters, such as throttle position/opening, injection and ignition timings (i.e., duration, phase, etc.), and the like. One such map—a “torque map”—allows an operator to manage the engine drivability through the redefinition of torque delivery by the vehicle's engine. The torque map is a two-dimensional table with engine speed (e.g., velocity or revolutions per minute (RPMs)) and throttle or accelerator pedal position measured using an accelerator pedal position sensor (APS) as inputs and torque as the output.
An operator can manipulate a vehicle's torque map to define the torque behavior of the vehicle. For instance, FIGS. 1A-1C illustrate exemplary hypothetical torque maps 100 resulting in different engine behaviors. Each torque map 100 includes multiple APS lines indicating a range of accelerator (or gas) pedal positions (e.g., 10% APS equates to the accelerator pedal being 10% depressed, 100% APS equates to the accelerator pedal fully depressed, etc.). Following a particular APS line and engine speed in RPMs (x-axis) as inputs, the torque map 100 outputs a corresponding amount of torque (y-axis).
As shown in FIG. 1A, the engine outputs a constant torque. That is, for all RPM values, the torque produced by the engine remains constant for a given APS. On the other hand, as shown in FIG. 1B, the engine outputs a constant power. As is known in the art, power is the product of torque multiplied by a rotational speed, in this case, RPM. Thus, as the RPMs of the engine increase, the torque produced by the engine decreases proportionally, and vice versa, so as to output a constant power. As a result, even as APS remains constant, the slope of the APS lines change due to the changing torque. As shown in FIG. 1C, a hybrid approach combining the constant torque and constant power torque maps can be used. Here, the torque strategy resembles constant torque at low- and high-RPMs and constant power at mid-RPMs. It should be apparent that vehicle torque maps can be shaped in a range of ways to affect the drive behavior of the vehicle, e.g., making the vehicle feel sportier, increasing the vehicle's hauling capabilities, etc.
Torque maps are formulated for each of the vehicle's gears. To this end, a base torque map can be defined (in first gear, for example), and a factor can be applied to the torque values in each APS position of the base map to establish torque maps in other gears. For instance, FIG. 2 illustrates an exemplary hypothetical torque map factor table 200 containing factors (the factor for first gear is 1, since first gear is the base torque map) by which to multiply the torque output at varying APS positions for each gear. Thus, after defined the base torque map in one gear, torque maps can be easily defined in subsequent gears using the factor table 200.
Meanwhile, gear shift patterns or schedules dictate the driving conditions under which a vehicle changes gears—either upshifting or downshifting. In automatic transmission vehicles, a vehicle control unit, e.g., a transmission control unit (TCU), can control the gear shifting based on throttle opening and vehicle speed/engine RPM as inputs. For instance, FIG. 3 illustrates an exemplary hypothetical gear shift pattern 300 showing shift shapes for each gear. Here, a vehicle gear is shifted according to the throttle opening and engine RPM. For a given throttle in a given gear, there is a unique vehicle speed at which a shift takes place. Notably, the gear shift pattern 300 depicts a downshift pattern, specifically; though the procedure operates similarly for upshifting.
Shift patterns are typically created taking into account fuel economy, engine capability, and performance drivability. In the gear shift pattern 300, fuel economy is considered by the minimum lines 310 in the shift pattern. Conversely, the maximum lines 320 are established knowing the engine's performance capability. Further, the mid-pedal region 330 can be adjusted to achieve a desired response or feel. Common practice involves adjusting a vehicle's shift pattern to address drivability concerns, such as sluggish acceleration where the vehicle does not adequately respond to a driver depressing the gas pedal, busy shifting, and the like.
Like manipulation of a vehicle torque map, manipulation of a gear shift pattern can modify the drive behavior of a vehicle. However, adjusting the torque map without regard for the gear shift pattern, or vice versa, can create drivability issues, mainly due to the gear ratios. For instance, engine response can feel sluggish during accelerator pedal tip-in due to torque saturation (i.e., the engine has reached the maximum amount of available torque in a current gear). That is, the driver cannot feel a level of acceleration in the vehicle's current gear. The problem arises because there is no feeling of torque reserve in all gears. Also, after a downshift, the immediate acceleration response can feel excessive and jolt the driver and passengers. The result is a driving experience that feels discontinuous and unpredictable.